SpringMVC 源码之网络请求(4)

发表于 更新于 分类于

DispatcherServlet#processDispatchResult

定位: org.springframework.web.servlet.DispatcherServlet#processDispatchResult

处理 ModelAndView; 或者将异常转换为 ModelAndView 

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private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
        @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
        @Nullable Exception exception) throws Exception {

    // 标记是否为处理生成异常的ModelAndView对象
    boolean errorView = false;

    // 如果请求处理过程中有异常抛出则处理异常
    if (exception != null) {
        // 从ModelAndViewDefiningException中获得ModelAndView对象
        if (exception instanceof ModelAndViewDefiningException) {
            logger.debug("ModelAndViewDefiningException encountered", exception);
            mv = ((ModelAndViewDefiningException) exception).getModelAndView();
        }
        // 处理异常，生成ModelAndView对象
        else {
            Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
            mv = processHandlerException(request, response, handler, exception);
            errorView = (mv != null);
        }
    }

    // Did the handler return a view to render?
    // 是否进行页面渲染
    if (mv != null && !mv.wasCleared()) {
        // 渲染页面
        render(mv, request, response);
        // 清理请求中的错误消息属性
        // 因为上述的情况中，processHandlerException会通过WebUtils设置错误消息属性，所以需要进行清理
        if (errorView) {
            WebUtils.clearErrorRequestAttributes(request);
        }
    }
    else {
        if (logger.isTraceEnabled()) {
            logger.trace("No view rendering, null ModelAndView returned.");
        }
    }

    // 如果启动了异步处理则返回
    if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
        // Concurrent handling started during a forward
        return;
    }

    // 发出请求处理完成通知，触发Interceptor的afterCompletion
    if (mappedHandler != null) {
        // Exception (if any) is already handled..
        mappedHandler.triggerAfterCompletion(request, response, null);
    }
}

DispatcherServlet#processHandlerException

定位: org.springframework.web.servlet.DispatcherServlet#processHandlerException

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protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
        @Nullable Object handler, Exception ex) throws Exception {

    // Success and error responses may use different content types
    // 移除 PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE 属性
    request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

    // Check registered HandlerExceptionResolvers...
    // 遍历 HandlerExceptionResolver 数组，解析异常，生成 ModelAndView 对象
    ModelAndView exMv = null;
    if (this.handlerExceptionResolvers != null) {
        // 遍历 HandlerExceptionResolver 数组
        for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
            // 解析异常，生成 ModelAndView 对象
            exMv = resolver.resolveException(request, response, handler, ex);
            // 生成成功，结束循环
            if (exMv != null) {
                break;
            }
        }
    }
    // 情况一，生成了 ModelAndView 对象，进行返回
    if (exMv != null) {
        // ModelAndView 对象为空，则返回 null
        if (exMv.isEmpty()) {
            request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
            return null;
        }
        // We might still need view name translation for a plain error model...
        // 没有视图则设置默认视图
        if (!exMv.hasView()) {
            String defaultViewName = getDefaultViewName(request);
            if (defaultViewName != null) {
                exMv.setViewName(defaultViewName);
            }
        }
        // 打印日志
        if (logger.isTraceEnabled()) {
            logger.trace("Using resolved error view: " + exMv, ex);
        }
        else if (logger.isDebugEnabled()) {
            logger.debug("Using resolved error view: " + exMv);
        }
        // 设置请求中的错误消息属性
        WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
        return exMv;
    }
    // 未生成 ModelAndView 对象，则抛出异常
    throw ex;
}